The invention relates to a breech device of a hand firearm, comprising a firearm casing with a slidingly arranged carrier with a breech block, which comprises a slidingly arranged firing pin with a striker, wherein a locking arm is pivoted in the rear portion of the carrier.
A locking mechanism is known from the patent documents CZ 58598 and CZ 59377 (Frantisek Janecek et al.), wherein the locking mechanism functions from the so called back position, which means that whole of the breech device is in the back position before the shot. In such a mechanism the striker is fixed to the carrier of the breech block and a shot is fired only after a complete locking. Such a construction of the whole locking mechanism is not preferred because the breech device has to be unlocked and the return springs have to be fully tensioned if the fire arm is to be prepared for shooting. Because of the impact of the relatively huge mass of the breech device the aiming of the firearm is disturbed, especially in the semi automatic firing mode. Another locking mechanism is known from U.S. Pat. No. 2,270,683 (Frantisek Janecek) which is to work from the front position. The '683 patent discloses a locking device consisting of a breech block and a carrier which are arranged slidingly with respect to each other and which are connected by a single-arm lever, the lever being pivoted in the carrier and its free end being supported by the tail part of the breech block. At the same time, the free end of the single-arm lever is formed to engage a stop formed at the breech block casing. There is a through opening formed in the lever for an introduction of the hammer which actuates the cartridge by hitting the firing pin with the striker.
Practical experience with such a mechanism has shown that its use in current hand firearms is limited. The mechanism cannot be effectively used for fully automatic firing mode, if the firing is to be performed with the breech block having been locked and a trigger and hammer device is to be used to fire off the cartridge. The interaction of the components of the breech block and the interaction of the components and of the breech block casing is disadvantageous. During the locking of the cartridge chamber the breech block recoils backwards significantly, more specifically in that moment when the breech mechanism reaches the front position, i.e. the locking position, and when the gear ratio of the single-arm lever (the so called accelerator) is fully used to increase the locking force for a proper and safe locking of the cartridge chamber. After the impact, the carrier of the breech block recoils, wherein the single-arm lever is pivoted in the breech block and is subjected to bending within the elastic deformation region during the final phase of locking the cartridge chamber. Also the side walls of the breech block casing between the cartridge chamber and the stop are subjected to tension within the elastic deformation region. During the locking, the breech block, too, is subjected to buckling within the elastic deformation region. Any springing of the material of the breech device and of the casing material is amplified by the gear ratio of the single-arm lever. The extent of the recoil depends especially on the gear ratio of the single-arm lever, on the tension of the return spring, on the elastic modulus of the materials, of which the respective components of the breech device and the casing are made, on the weight of the carrier of the breech block, on the frictional resistance of the sliding components of the breech device, and on the angle of inclination of the firearm, i.e. elevation or depression.
Any substantial recoil of the breech device is unacceptable because the firing of the cartridge is executed too early, specifically at the time when the cartridge chamber has not been fully locked yet. Such firing causes a loss of the fully automatic function of the firearm. It may also cause a destruction of the bottom of the cartridge because the pressure of the gases at the time of recoil pushes the cartridge out of the cartridge chamber such that a part of the cartridge wall gets outside the cartridge chamber into a free unprotected space where the unprotected part of the wall of the cartridge will not resist the pressure of the gases inside the cartridge. So the unprotected wall of the cartridge is destroyed and the leaking gas expands and the mechanism of the hand firearm as well as the health of the shooter may be affected.
The disadvantages and deficiencies of the firearm as disclosed in U.S. Pat. No. 2,270,683 are eliminated at least partially by the locking mechanism of a hand firearm disclosed in the Czech patent application No. CZ PV 341-2006 (Ladislav Findorak). The unwanted recoil of the carrier of the breech block, which may cause a faulty locking of the cartridge chamber, is prevented by an increased clearance between the cross stop of the firearm casing and the locking lever. For such a construction, the longitudinal shaping of the locking lever in the breech block carrier is essential. As described in the Czech patent application, the primer of the cartridge is actuated by the striker, which transmits the power from the hammer. Although the recoil of the breech block carrier is lower compared with the previously described mechanism, the recoil is still objectionable, especially if the firearm is to function properly in the fully automatic mode. Tests have shown that if the clearance between the locking arm and the cross stop in the firearm casing is larger than an assembly clearance, which is about 0.2 millimetres depending on the gauge of the firearm, so-called tapping at the cross stop occurs during the shooting. The tapping increases the running clearance and lowers the locking power, which results in higher and higher velocities of the breech masses over the working life of the breech device. When the above described clearances are larger than the allowable assembly clearances, the locking lever is in an unidentified position before the shooting due to the shaping of the seat of the lever and the lever's heavier weight and inertia. As shown in CZ PV 341-2006, where the clearances are larger than the assembly clearances, upper nose 49 of the single arm release lever 50 of the hammer pushes the single arm transmission lever 37, i.e. the locking lever, up because of the operation of the spring 52.
Before the firing, the single arm transmission lever 37 is seated in an unknown position due to the clearances and allowed shaping, and it has to be seated in the working position within a split second under extreme forces. Undesirable seating of the lever is also caused by the weight increase caused by the added nose for the hammer. The single arm release lever 50 with its spring acts in the direction opposite to its movement during the locking. The larger the added clearance between the lever and the cross stop of the firearm casing, the larger the overall clearances. During the firing, the locking lever has to get in its working position so that the tapping occurs within a split second and under extreme forces. An unwanted wear of the locking arm seat occurs in the device according to CZ PV 341-2006, and there is a risk of breaking the lever due to the excessive load applied for a very short time. According to practical experience, the recoil in the mechanism is markedly lowered, but it is not fully eliminated, because there is always a reaction when two elements strike against each other at high speed and with a heavy force. The device comprises a securing element to secure the locking of the breech device, and the securing element may recoil in a larger degree in the fully automatic mode of firing and therefore may affect the reliability unfavourably. This occurs because it is practically impossible to time the stroke of the hammer upon the firing pin in the first phase of locking the breech device before the recoil.
Another disadvantage of the device is the seating of the locking device in the carrier of the breech block. Moving backwards, the carrier takes the breech block by being connected by the locking arm, so that the breech block is subject to a buckling load. At the time of striking, the back of the breach block is subject to a pressure load, such that an extraordinary technology of hardening and machining is required, otherwise the breech block may break.